1. Field of the Invention
This invention relates in general to organometallic liquid absorbents and absorption heat pumps and related refrigeration and air conditioning technology that provide environmentally clean and highly efficient heating and cooling for buildings and processes.
2. Background
The heating, ventilating, air conditioning and refrigeration (HVACandR) industry has been undergoing momentous change due to the Montreal Protocol that dictated replacement of environmentally damaging chlorofluorocarbon (CFC) refrigerants. Manufacturers of refrigeration equipment have been converting to less environmentally damaging HCFC and HFC refrigerants, but these must also be phased out because they are not totally benign. However, the industry is uncertain as to which of the new refrigerants are the best choices for future systems. In Europe the HVACandR industry is converting to hydrocarbon (HC) refrigerants including propane and isobutane, but these are flammable and are not allowed indoors by U.S. Building Codes. The 1997 Kyoto Protocol committed the U.S. and most of the industrialized world to substantial reductions in CO2 production and other greenhouse gas emissions within the near future. Also, the industry is being pressed by government regulations, by electric utilities and by customers to make their refrigeration products more efficient. In many parts of the world, where there is a shortage of electric power, electric utilities are providing incentives for more efficient systems and in some areas heat driven systems are required. In the U.S., federal research to develop more efficient buildings and appliances has been increased and incentives, including tax credits, are being proposed for more efficient appliances including heat pumps and air conditioners.
Clearly, there is a pressing worldwide need and a huge opportunity for the HVACandR industry to provide more efficient and environmentally clean technology for heat pumps, air conditioners, refrigerators and process heating and cooling systems.
A number of solid absorbent heat pump technologies have been investigated, including metal hydrides, silica gels and carbon absorbents, but such granular solids have poor heat transfer and must be used in fixed reactor vessels having high heat capacity. The efficiency of such solid absorbents heat pump systems suffer from the large parasitic heat losses associated with thermal cycling of these high heat capacity reactor vessels.
Liquid absorbents have substantial advantages over solid absorbents because liquids can be pumped and have superior heat transfer properties, which are large advantages for refrigeration equipment. Common liquid absorbent combinations such as ammonia/water and lithium bromide/water have been used for many years. The lithium/bromide systems suffer from corrosion and crystallization. The generator-absorber heat exchange (GAX) heat pump, which is an improved version of the old xe2x80x9cServelxe2x80x9d ammonia/water absorption heat pump, has received substantial government funding because it offers up to 50% improvement in efficiency over typical absorption heat pumps today. However, ammonia is toxic and flammable and is not compatible with copper which is commonly used in refrigeration systems. Further, the GAX heat pump was rejected by its early HVACandR industry licensee due to its complexity and relatively high cost.
It is with the large worldwide need and the shortcomings of the existing art in mind that the significant improvements and advancements of the present invention were developed. Following are publications that are referred to below.
Crabtree, R. H. 1990. Dihydrogen complexes: some structural and chemical studies. Accounts of Chemical Research 23: 95-100.
Heinekey, D. M. and W. J. Oldham. 1993. Coordination Chemistry of Dihydrogen. Chemical Reviews 93: 913-926.
Kubas, G. J. 1988. Molecular hydrogen complexes: coordination of a "sgr" bond to transition metals. Accounts of Chemical Research 21: 120-128.
Sellmann, D. 1971. Oxidation of C5H5Mn(CO)2N2H4 to C5H5Mn(CO)2N2, a New Dinitrogen Complex. Angewandte Chemie International Edition in English 10:919.
Sellmann, D. 1972. Reversible N2 Fixation by Dicarbonyl-1/4-cyclopentadienyl(tetra-hydrofuran)manganese(I). Angewandte Chemie International Edition in English 11: 534.
Strohmeier, W.; Barbeau, C.; and von Hobe, D. 1963. Photochemisch Reaktionen von Sauertoff-Donatoren mit Metallcarbonylen. Chemische Berichte 96: 3254-3259.
The environmentally clean liquid absorbents and the highly efficient absorption heat pump systems of the present invention have largely solved the problems mentioned above.
One broad aspect of the invention is a family of organometallic liquid absorbents that can reversibly absorb and desorb large amounts of gas. The hydrogen absorbing liquids are referred to as HySorb liquids and the nitrogen absorbing liquids as NiSorb liquids. When gas is absorbed in such liquids, an exothermic process occurs, and a large amount of heat of absorption is liberated. This heat may be used for space heating, process heating, water heating or other useful heating application. When gas is desorbed from such a liquid, an endothermic process occurs, providing a large amount of cooling due to the heat of desorption. This cooling effect can be used to produce refrigeration for a heat pump, air conditioner, refrigerator, icemaker, dehumidifier, electronics cooling system, process cooling or other cooling application. Such organometallic liquid absorbents can also be used to absorb and separate gases in industrial processes.
One HySorb organometallic liquid absorbent is (xcex75-C5H5)FeH(H2){P(CH3)3} which reversibly absorbs and desorbs hydrogen gas. We synthesized this HySorb liquid by a four step process from the starting material (C6H6)Fe(PMe3)2, which was prepared through metal atom vapor synthesis techniques.
One NiSorb organometallic liquid absorbent is {xcex75-C5H4(CH3)}Mn(CO)3(N2), which absorbs large quantities of nitrogen gas and which is used in combination with an exchange liquid to obtain specific thermodynamic properties. The exchange liquid can be selected from one or more members of a family of organic compounds, including tetrahydrofuran (THF), acetone and ether. A mixture of exchange liquids can also be used with the NiSorb liquid to obtain unique thermodynamic properties. The thermodynamic properties and miscibility of the NiSorb liquid can also be varied by modification of the chemical structure of the organometallic complex. For example, related complexes can be prepared by replacing the methylcyclopentadienyl ligand of the NiSorb liquid by other cyclopentadienyl, Cp, ligands such as: unsubstituted Cp, other alkyl (that is, ethyl, propyl, butyl) Cp; and Cp ligands containing functionalized alkyl groups (that is, C(O)OH, NH2, OR, NO2 SR, PR2 and SO3).
The NiSorb liquid can be prepared, for example, by a process beginning with the inexpensive starting material called MMT, {xcex75-C5H4(CH3)}Mn(CO)3, which is economical and commercially available in bulk quantities. Our process begins with photosubstitution of a carbonyl ligand of MMT by dinitrogen (N2). The process is carried out in a tetrahydrofuran (THF) solution, which produces the THF adduct {xcex75-C5H4(CH3)}Mn(CO)2(THF). The substitution of the THF ligand by dinitrogen and the removal of the THF solvent is accomplished by sweeping the solution with nitrogen gas. Purified NiSorb liquid is obtained in greater than 90% yield upon trap to trap distillation of the crude product en vacuo.
Another broad aspect of the invention is the absorption heat pumps that utilize the organometallic liquid absorbents to produce heating and cooling. The absorption heat pump comprises an absorber, desorber, liquid-to-liquid heat exchanger, liquid pump, pressure reducer, organometallic liquid absorbent, refrigerant gas, gas compressor, connecting liquid piping and connecting gas piping. The liquid absorbent is one member of the family of organometallic liquids with suitable thermodynamic properties and the refrigerant gas is a compatible gas that is readily absorbed by the liquid absorbent. The gas compressor desorbs refrigerant gas from the desorber at low pressure and compresses it into the absorber at higher pressure where it is absorbed. The liquid pump is adapted to be driven by external power to pump the organometallic liquid absorbent from the low pressure desorber through one side of the heat exchanger, through the absorber, back through another side of the heat exchanger, through the pressure reducer and back to the desorber. The liquid-to-liquid heat exchanger provides internal heat recovery from the organometallic liquid exiting the absorber and transfers this heat to the organometallic liquid exiting the desorber. The desorber provides cooling derived from the heat of desorption of the organometallic liquid absorbent and the absorber provides heating derived from the heat of absorption of the organometallic liquid absorbent. The absorber and desorber have suitable heat exchange means, such as finned surfaces and fans or liquid-to-liquid heat exchangers, thermostats and controls to allow them to transfer heat with their surroundings, which may be the ambient air or the indoor air. The gas compressor may be a mechanical gas compressor adapted to be driven by external power.
The gas compressor may also be a heat driven sorption gas compressor comprising a regenerator loop to provide the compressed refrigerant gas to the absorption heat pump. The regenerator loop has a unique organometallic liquid absorbent with suitable thermodynamic properties. The regenerator loop comprising an absorber, desorber, liquid-to-liquid heat exchanger, liquid pump, pressure reducer, organometallic liquid absorbent, refrigerant gas, connecting liquid piping and connecting gas piping. The desorber of the regenerator loop is heated to desorb the refrigerant gas to provide gas compression for the absorption heat pump. The liquid pump is adapted to be driven by external power to pump the organometallic liquid absorbent from the low pressure absorber through one side of the heat exchanger, through the higher pressure desorber, back through another side of the heat exchanger, through the pressure reducer and back to the absorber. The liquid-to-liquid heat exchanger provides internal heat recovery from the organometallic liquid exiting the desorber and transfers this heat to the organometallic liquid exiting the absorber. The absorber operates at low pressure to absorb gas from the desorber of the connected absorption heat pump where cooling is produced and heat rejected to the surroundings at near ambient temperature. The absorber of said regenerator loop has suitable heat exchange means to transfer heat with the surroundings, which may be the ambient outdoor air. The desorber has suitable heat exchange means so it may be heated by a gas-fired heater, a solar heater, a process heater, an electric heater or some other type of heater. These heat pumps can provide air conditioning, heating, refrigeration, ice making, dehumidification, electronics cooling, water heating and cooling, process cooling and heating or other useful heating and cooling.
Another broad aspect of the invention is a cryocooler comprised of a sorption gas compressor connected to a gas expander. The operation of this sorption gas compressor is the same as that in the heat driven sorption gas compressor described above. The absorber of the sorption gas compressor absorbs gas from the cryocooler outlet at low pressure and rejects heat to the surroundings at near ambient temperature. Its desorber is heated to desorb and provide higher pressure compressed gas to the gas expander. The gas being compressed by the sorption gas compressor is the same as the gas passing through the gas expander to be cryocooled. The gas expander comprises a control valve, at least one gas-to-gas heat exchanger, a Joule-Thompson expander, an optional turbo-expander, a cryocooler space and connecting gas piping. The connecting gas piping receives compressed gas from the sorption compressor desorber and the gas passes through an optional pre-cooler heat exchanger and control valve, where it is split into two streams. The first stream fraction passes through at least one gas-to-gas heat exchanger for further cooling and through a Joule-Thompson expander where it achieves cryo-temperatures in the cryocooler space. The remainder gas fraction exiting the control valve is cooled through at least one gas-to-gas heat exchanger and through an optional turbo-expander and at least one additional heat exchanger to provide pre-cooling for the primary gas stream before rejoining the primary gas stream. The combined gas stream passes through gas piping and an optional heat exchanger to provide gas pre-cooling and then exits through the connecting gas piping and enters the absorber of the sorption gas compressor. The cold gas may be liquefied in the cryocooler space. Hydrogen gas may be cryocooled when a HySorb liquid is used in the sorption compressor. Nitrogen gas may be cryocooled when a NiSorb liquid is used in the sorption compressor. Other gases may be cryocooled and possibly liquefied with suitable organometallic liquid absorbents in the sorption gas compressor.